Designers need to know this information to correctly work up photographs to be ready to print, and to accurately predict how the photo will look after printing.

This article explains the logic behind the different colors that the human eye can see, and how different colors are processed on photo-editing software such as Adobe Photoshop.

After you have read through this tutorial, read the differences between bitmaps, channels and the CMYK process in a more advanced article.

To take color one step further, read this article about different color systems, and how printers process color information. It also mentions how to layer colors for optimum printing.